Added HMAC and GCM en- and decryption
added encryption functions with nonce parameter
ctr mode test vectors are working
gcm mode test vectors are working
removed unused imports
added handling of nonce=null and counter.length=0
finally added second nonce=null handling
added comments for code understanding
Merge pull request #146 from roeslpa/apply_test_vectors

GCM and CTR mode with 96 bit nonce